Julius Peppers crouched into his stance and put his left hand on the Soldier Field grass to ready himself for the type of play on which the Bears' defense has forged its reputation for dominance.

It was third-and-10 from the Bengals' 9-yard line in the second quarter of the season-opener, an opportunity as good as any for the Bears to wreak havoc and, better yet, take the ball away. It was time to feast.

Instead of a sack or interception, though, it all went wrong. Peppers' left-handed slap didn't move Bengals second-string left tackle Anthony Collins. The Bengals stonewalled the Bears' four-man pass rush, and quarterback Andy Dalton comfortably lofted a perfect throw over cornerback Zack Bowman for a 21-yard completion near the left sideline.

Such letdowns are why the Bears' defense has the worst third-down conversion percentage in the NFL through two games. That's a major point of emphasis entering Sunday night's road game against the Steelers.

"We just have to rush better, we have to cover a little bit better and just have a general mindset of getting off the field," Peppers said. "It's never easy to get there, but it's definitely to the defense's advantage on third-and-long so we're going to have to do a better job to take advantage of those situations."

The Bears have surrendered a conversion on 14 of 27 third-down attempts this season, and that excludes Charles Tillman's defensive pass interference penalty that gave the Bengals an automatic first down on third-and-13 in the opener.

That 51.9-percent conversion rate is so unsettling to players and coaches because the Bears' defense historically shines on third down. It has been above 40 percent only once since 2000, and it has ranked in the NFL's top 10 in each of the last three seasons.

On Sunday night, though, they face an offense that has struggled in the same area. The Steelers have converted 7 of 25 third downs, the league's third-worst rate.

"You think about when you're struggling on third down, you look and you don't necessarily have to try to fix third downs," Steelers quarterback Ben Roethlisberger said. "You have to fix first and second down, so you're not putting yourself in third-and-long situations so much."

Truth is, the Steelers haven't been good on third-and-short, either. They're 1-for-10 on third-and-5 or shorter. That represents an opportunity for the Bears to cure their greatest ailment.

Third down woes always are complex, as Bears defensive coordinator Mel Tucker reminded reporters Wednesday. Defensive linemen must generate pressure to help the defensive backs in coverage, and vice versa.

The pass rush is a major factor, and the Bears are not satisfied with theirs. They have only two sacks through two games, but that's only part of the problem. In addition to staying upright, opposing quarterbacks have had time to survey the field comfortably, as Dalton did on that third-and-10 conversion in Week 1.

"This week it's going to be improved," Peppers said. "I'm not interested in talking about anything from last week. My focus is on Pittsburgh and getting better."

This week, that means containing Roethlisberger. At 6 foot 5, 241 pounds, tacklers regularly slide off him as if his uniform were made of Teflon.

"There's a lot of faster quarterbacks in the league, but I don't know that there has been one any better over the last decade at extending plays under the chaos of a pass rush better than Ben Roethlisberger has done it," Bears coach Marc Trestman said.

Tucker and Trestman emphasized the need for Bears pass rushers to stay in their lanes. Breakdowns in that area last Sunday against the Vikings led to problems on third downs. Vikings quarterback Christian Ponder scrambled for one first down and set up a fourth-down conversion with another.

When the Bears defense practices its third-down game plan Thursday, the focus among the linemen will be clear.

"We need to finish our rushes," Tucker said. "We were getting closer but no cigar. This week is about finishing."